Superficial topical infections are typically a consequence of a primary disease source such as chronic urinary incontinence, or are directly related to a contagious nosocomial or endemic source. Prolonged moist or wet skin conditions often lead to maceration and other changes in skin integrity which provide the opportunity for normally saprophytic bacteria and fungi to invade the site and establish an infection.
The microorganism most prevalent in the moist environment of a skin infection is Candida albicans, a yeast-like fungus. This type of infection is usually characterized by erythema, edema and intense pruritus. Other localized, topical infections that are bacterial in origin may be the direct result of skin-to-skin contact with a contaminated vector. One of the most serious nosocomially acquired contagious bacterial infections is methicillin resistant Staphlococcus aureus which is often implicated in skin cellulitis, impetigo, boils and wound infections. On occasion, the etiological agent of the infection is a combination of bacteria and fungi. This is referred to as a mixed infection, wherein dissimilar microorganisms coexist to both the benefit of and the detriment to the host.
In more serious maladies of the dermis wherein the skin is breached, especially in chronic wounds and ulcers, a variety of micro-organisms, both pathogenic and non-pathogenic, contaminate the site of the breach. Non-pathogenic microorganisms constitute the normal flora of intact skin, but these can become pathogenic when their numbers overwhelm the natural host defenses in a wound environment, and subsequently cause infection.
Quantitatively, it has been shown by Kucan et al., that open wounds can maintain a bioburden of approximately 10.sup.5 microorganisms per gram of tissue without the clinical manifestation of infection. "Comparisons of Silver Sulfadizine and Physiologic Saline in the Treatment of Chronic Pressure Ulcers." Amer. Ger. Soc. 29:232-235, 1981. However, a bioburden of greater than 10.sup.5 is a significant challenge for the local wound tissue defenses. Consequently, a bioburden of 10.sup.6 microorganisms per gram will often result in wound infection.
Wounds that are heavily contaminated by microorganisms, but not clinically infected, are often characterized by a prolonged period of inflammation, as well as a delay in wound repair and healing. Microorganisms that contaminate wounds have been implicated as an important factor in the retardation of wound healing by interfering with leucocyte phagocytosis, and by the depletion of nutrients and oxygen required for normal tissue granulation. Ree et al., "Cutaneous Tissue Repair: Practical Implication Of Current Knowledge, Part II." Jour. of the Amer. Academy of Dermatology 13(6):919-941, 1985.